In radio communication networks, such as the Long Term Evolution (LTE) or the LTE-Advanced (LTE-A) of the 3rd Generation Partnership Project (3GPP), network planning includes usage of base stations. A User Equipment (UE) may communicate with another UE through the base station(s). Alternatively, it is proposed that the UEs may communicate directly by applying resources configured by the network for a Device-to-Device (D2D) communication.
The D2D communication enables discovery and data communication services between the UEs. Discovery is a process which determines that a D2D-enabled UE is in proximity of another D2D-enabled UE. A discovering D2D-enabled UE determines whether or not another D2D-enabled UE is of interest to it using D2D discovery. A D2D-enabled UE is of interest to a discovering D2D-enabled UE if the UE's proximity needs to be known by one or more authorized applications on the discovering D2D-enabled UE. In an example, a social networking application can be enabled to use D2D discovery feature. The D2D discovery enables the D2D-enabled UE of a user of a social networking application to discover and be discoverable by the D2D-enabled UEs of his/her friends. In another example, the D2D discovery can enable the D2D-enabled UE of the user of a search application to discover stores/restaurants and so on of the user's interest in the user's proximity. The D2D enabled UE discovers other D2D-enabled UEs in the UE's proximity using direct UE-to-UE signaling.
In existing systems, the D2D communication is supported when the D2D enabled UE's are in the same PLMN, i.e., for example, the D2D enabled UE can discover another D2D enabled UE belonging to the same PLMN as that of the discovering D2D enabled UE. The D2D enabled UE cannot discover another D2D enabled UE, when another D2D enabled UE belongs to a different PLMN as that of the PLMN of the D2D enabled UE. Hence, in the existing systems, the D2D communication is only supported when both the D2D enabled UEs belong to the same PLMN.
Further, discovering another D2D enabled UE which belongs to a different PLMN as that of the D2D enabled UE is cumbersome due to following reasons as described herein. Consider a scenario, in which a D2D UE announcing the discovery signals in a cell of a PLMN X. The PLMN X can be the home PLMN or visited PLMN for the D2D UE. The D2D UE monitoring the discovery signal is in a cell of PLMN Y. The PLMN Y can be the home PLMN or visited PLMN for the monitoring D2D UE. During monitoring, the D2D UE has to monitor multiple frequencies (belonging to different PLMNs). The D2D UE monitors the frequencies of all the PLMNs which the D2D UE is authorized to monitor.
Further, the D2D UE monitors the D2D discovery signal in idle state. In order to monitor discovery signal on multiple frequencies of different PLMNs, the D2D UE's wakeup time will significantly increase. In connected state the D2D UE needs gaps to monitor the discovery signal. Also, monitoring different frequencies of different PLMNs requires more gaps which may have significant impact on the communication of the D2D UE with a serving cell of the D2D UE in the UE's PLMN.
The above information is presented as background information only to help the reader to understand the present disclosure. Applicants have made no determination and make no assertion as to whether any of the above might be applicable as Prior Art with regard to the present application.